1. Field of the Invention
This disclosure relates to an exposure device, an image formation apparatus, and a method of manufacturing an exposure device.
2. Description of Related Art
An electrophotographic image formation apparatus, such as a printer, a copier, a facsimile machine, and a multifunction machine, is equipped with an exposure device, which forms an electrostatic latent image on a surface of an image carrier (a photoconductor drum) by irradiating the surface with light.
The exposure device includes a board on which light emitting diodes (LEDs) being light emitting elements are arranged, a lens array disposed opposite to the board, and a holder which holds the board and the lens array. The holder includes an opening to which to attach the lens array, and aboard contact surface formed at a predetermined interval from the lens array in an optical axis direction. A distance between the LEDs on the board and the lens array is determined by placing the board on the board contact surface (see Japanese Patent Application Publication No. 2009-73041 (paragraphs 0022 and 0025, and FIG. 1)).
The holder is generally made of an aluminum die-cast body, and the board contact surface is formed by machining. In general, a flatness of the board contact surface is about 20 μm.